1. Field of the Invention
The present invention relates to a communication terminal apparatus for communication among multiple locations.
2. Related Background Art
Efficacy of communication terminals utilizing communication channels, such as television conference terminals, is attracting attention in recent years, from the standpoint of reduction of costs of business trips and of effective utilization of time. Also, there is being developed a multi-point television conference system with multi-point function for conducting a conference among multiple locations, in addition to point-to-point function for conducting a conference between two points.
In such multi-point television conference system, the communication among multiple locations is generally realized by a multi-point control unit (MCU), but there is recently developed a system capable of realizing the communication among multiple locations without the MCU, by connecting plural information channels to the different television conference terminals and connecting the information channels so as to form a loop or a bus.
In such television conference system, in the point-to-point mode, various display modes may be realized on each display unit such as (1) display of a received image over the entire image frame, (2) graphic display over the entire image frame, with a window display therein of the received image, or (3) combined display of the own image and the received image on graphic display, and such initial setting may also be suitably varied. Also in the multi-point mode, there can be increased the number of received images to be displayed, in addition to the display modes in case of the point-to-point mode.
FIG. 4 is a block diagram of such conventional multi-point television conference terminal, wherein a camera 1, serving as the image input means of the terminal, is used for entering the image of the user of this terminal or a drawing. A display unit 2, for displaying the input image data from the camera 1 or the image data received from another terminal, is composed for example of a CRT (cathode ray tube) or a LCD (liquid crystal display device). A video input interface unit 3 effects switching of the image input means (camera 1), A/D (analog-to-digital) conversion of the image data, conversion of image data size, transformation of image data format, etc. under the control of a system control unit 11 to be explained later.
A video output interface unit 4 is composed of a received image scaling unit 4a for converting the image size of received image data, an image memory unit 4b for temporarily storing the image data at the image size conversion by the received image scaling unit 4a, an image memory control unit 4c for controlling the image data write-in into and image data read-out from the image memory unit 4b, and a TV signal encoding unit 4d for converting the image data, read from the image memory unit 4b, into television (TV) signals under the control of said image memory control unit 4c. 
A video encode/decode unit 5, for encoding the transmission image signal and decoding the received image signal according to the recommendation H.261 of ITU-T (former CCITT: Consultation Committee for International Telegraph and Telephone), is composed of a video encoding unit 5a and a video decoding unit 5b. There are also provided a handset 6 serving as voice input/output means of the present terminal, a microphone/speaker 7 serving as another voice input/output means of the present terminal, and an voice input/output interface unit 8 for effecting echo cancellation in the use of the handset 6 or the microphone/speaker 7, generation of various tones, such as dialling tone, calling tone, busy tone, call arrival tone, etc., and switching of the voice input/output means (handset 6 and microphone/speaker 7) under the control of the system control unit 11.
A voice encode/decode unit 9, composed of a voice encoding unit 9a and a voice decoding unit 9b, effects encoding of the transmission voice signal and decoding of the received voice signal according to voice encoding/decoding algorithms such as 64 kbps PCMA-law, 64 kbps PCMxcexc-law, 64 kbps/56 kbps/48 kbps SB-ADPCM, 32 kbps ADPCM, 16 kbps (for example, LD-CELP) or 8 kbps under the instruction by the system control unit 11. An input unit 10, for entering control information for the entire control of the present terminal, is composed of a keyboard, a touch panel, a mouse, etc.
A system control unit 11 is provided with a CPU (central processing unit), a ROM (read-only memory), a RAM (random access memory), an auxiliary memory device, etc. and serves to monitor the status of various units, to prepare a display image according to the state of control of the entire terminal and to effect the execution of the application program. A demultiplex/multiplexing unit 12 effects multiplexing the voice signal from the voice encoding unit 9a, the image signal from the video encoding unit 5a and the control signal from the system control unit 11 in the unit of each transmission frame according to the ITU-T recommendation H.261 and demultiplexing of each received frame into the constituting media for transmission to various units. There are also shown a line interface unit 13 for line control according to an ISDN user network interface, and a communication line 14 such as ISDN.
In the following there will be explained the function of the multi-point television conference terminal of the above-explained configuration.
Input image from the camera 1 is supplied through the video input interface unit 3 to the video encoding unit 5a. Also, input voice from the handset 6 or the microphone/speaker 7 is supplied through the voice input/output interface unit 8 to the voice encoding unit 9a. The input image encoded in the video encoding unit 5a, the input voice encoded in the voice encoding unit 9a, and a control signal from the system control unit 11 are multiplexed in the unit of each transmission frame by the demultiplex/multiplexing unit 12, and are supplied through the line interface unit 13 to the communication line 14.
A received frame from the communication line 14 is transmitted through the line interface unit 13 and separated in the demultiplex/multiplexing unit 12 into the image signal, voice signal and control signal, which are respectively supplied to the video decoding unit 5b, the voice decoding unit 9b and the system control unit 11. The received image data, decoded in the video decoding unit 5b, are transmitted through the video output interface unit 4 and displayed on the display unit 2. Also, the received voice, decoded in the voice decoding unit 9b, is transmitted through the voice input/output interface unit 8 and is released from the handset 6 or the microphone/speaker 7.
The function of the video output interface unit 4 will be explained in further details. The received image data, decoded in the video decoding unit 5b, are stored in the image memory unit 4b. The received image data have a certain image size for each frame. The image size scaling is unnecessary if the image size is equal to that of the TV monitor of the display unit 2, but the image sizes are usually different. In order to mutually match the image sizes, the received image data stored in the image memory unit 4b are read under the control of the image memory control unit 4b according to the method of image size conversion and are supplied to the received image scaling unit 4a. 
The received image scaling unit 4a effects conversion of the image size according to a predetermined method, and the converted image data are stored in the image memory unit 4b again under the control of the image memory control unit 4c. The image data, thus stored in the image memory unit 4b, has an image size equal to that of the TV monitor. The image data, stored in the image memory unit 4b with the display image size of the TV monitor, are read under the control of the image memory control unit 4c and are supplied to the TV signal encoding unit 4d, which effects signal conversion and addition of various synchronization signals and burst signals, for enabling display on the TV monitor, thereby forming TV signals. In this manner the received image data are displayed on the TV monitor of the display unit 2.
In the following there will be explained a specific example of the function of such video output interface unit 4. For example, in the encoding method based on the ITU-T recommendation H.261, the frame size of the received image data is either in the FCIF mode of 352xc3x97288 pixels or in the PCIF mode of 176xc3x97144 pixels. In the following there will be considered a conversion method for displaying on a NTSC-TV monitor. FIG. 5 shows the concept of function, wherein image data of 352xc3x97288 pixels are stored in the image memory unit 4b. A horizontal line of 352 pixels is read, and dummy data (for example, black level data) of 4 pixels are added to each end to obtain data of 360 pixels. Then, between every two neighboring pixels, there is inserted a pixel of a value equal to the additive average of those of pixel of a value equal to the additive average of those of the two neighboring pixels. Finally, a dummy pixels (for example of black data) is added to the right-hand end. In this manner completed is the conversion from 352 pixels to 720 pixels.
The conversion for the vertical lines is conducted in the following manner. Since the TV monitor effects display by interlaced scanning, the 288 lines in the vertical direction are converted into 480 lines of a frame by line interpolation (insertion of 2 lines for every 3 lines), and the 480 lines are divided by the odd-numbered and even-numbered lines into two fields, for supply to the TV signal encoder 4d. It is also possible to prepare the data of a field by skipping 288 lines to 240 lines (by skipping 1 line for every 6 lines) and to repeat the same field twice at the interlaced scanning display. However, the deterioration of the image quality becomes conspicuous in case the same field is repeated twice because every two lines are the same in the display on the TV monitor, so that interpolation or filtering may be used in combination at the display of each field.
The above-explained conversion process enables the display of the image data of 352xc3x97288 pixels on the TV monitor. Naturally, other methods are also available for conversion.
FIGS. 6 to 8 illustrate the mode of multi-point television conference utilizing a multi-point control unit (MCU) 16, which is connected, through communication lines 14 and a network 17, directly with multi-point television conference terminals (1st to 4th terminals in FIGS. 6 to 8) of multiple locations to participate in the communication (cf. FIG. 6), and which synthesizes or selects the image data received from the locations, reconstructs the image data and distributes the image data to the multi-point television conference terminal at multiple locations. The multi-point television conference terminal of each location receives the image data distributed from the MCU 16 and displays, on the TV monitor constituting the display unit 2, an image corresponding to the received image data. Thus, if the received image data are limited to those of only one location, such image data of one location alone are displayed on the TV monitor (FIG. 7). On the other hand, if the received image data are synthesized from those of multiple locations, the image data of such multiple locations are displayed on the TV monitor (FIG. 8). Thus, each multi-point television conference terminal depends on the MCU 16 with respect to the display of the image data on the TV monitor, without any particular process on the side of the terminal.
In the conventional communication terminal apparatus such as the multi-point television conference terminal explained above, source locations are not identified in the image data of multiple locations at the display of the received image data on the TV monitor, so that it has not been possible to display, on the TV monitor, the image data of an arbitrary location or arbitrarily selected plural locations.
Also in the conventional multi-point television conference terminal explained above, in case of multipoint communication for receiving the image data of multiple locations by plural frames, it has been impossible not only to display the image data of an arbitrary location only on the TV monitor but also to collectively display the received image data of multiple locations on the TV monitor.
Another configuration of the television conference system consists, as shown in FIG. 8, of a loop-shaped connection of the lines 14 among the television conference terminals of multiple locations. In such television conference with the loop-shaped line connection, the display on the monitor of each terminal is conducted according to the initial setting, regardless of the state of connections of the multiple locations. Therefore, from the display windows on the display unit, showing the images from the multiple locations, the observer can know the participants connected to the system but cannot know the state of connection as a loop or a bus.
Such drawback is not limited to the television conference system but can occur likewise in the telephone conference for transmitting the voice only.
In consideration of the foregoing, an object of the present invention is to provide a communication terminal capable of resolving the drawbacks mentioned above.
Another object of the present invention is to provide a communication terminal capable of displaying the image of an arbitrary location, among the received images of multiple locations.
Still another object of the present invention is to provide a communication terminal capable of allowing display of the identification of the mode of connection of the communication terminals.
The foregoing objects can be attained, according to a preferred embodiment of the present invention, by a communication terminal apparatus for effecting communication among multiple locations by displaying image data on display means, comprising input means for entering information for designating image data of an arbitrary location, among the image data of the multiple locations, and control means for effecting control so as to display, on the display means, the image data of a location corresponding to the information entered by the input means.
Still another object of the present invention is to provide a communication terminal provided with novel functions.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following detailed description, to be taken in conjunction with the attached drawings.